This invention relates to improvements in traffic radar devices for law enforcement and related applications in which the speed of a target vehicle is detected from a stationary or moving transmitter location and, in particular, to a method and apparatus for processing Doppler return information by analyzing a limited area of the frequency spectrum corresponding to the speedometer output of the patrol vehicle, in conjunction with analysis of the entire frequency spectrum in order to improve target identification and minimize interference and unwanted harmonics.
In previous traffic radars utilizing digital signal processing (DSP), the patrol speed is found by using frequency and magnitude criteria, signal patterns, and patrol vehicle tracking history. Such a DSP radar is disclosed, for example, in U.S. Pat. No. 5,528,246 to Henderson et al., owned by the assignee herein. Anomalies can occur using these methods such as when the transmitting antenna is released from standby mode, when strong returns from other vehicles are received that are caused by a shadowing effect when a vehicle is traveling in the same direction as the patrol vehicle but at a different speed or when the patrol vehicle signal is summed with another vehicle moving in the opposite direction. Another problem can occur when the radar is in moving mode and the patrol vehicle comes to a stop at a traffic light. A return from moving traffic can be confused with the patrol vehicle and a wrong patrol vehicle speed is displayed resulting in an inaccurate calculation of a target speed.